Can Bird Flu in Milk Affect Humans?

Bird flu, formally known as avian influenza H5N1 (HPAI) virus, has been present since the 1990s, primarily affecting wild birds and poultry. In 2024, however, something unusual happened—the virus was detected in U.S. dairy cattle. Soon after, traces of H5N1 genetic material were found in pasteurised cow’s milk on grocery shelves. This raised a worrisome question: can drinking milk expose humans to bird flu (1^✔ ✔Trusted Source
Repeated oral exposure to H5N1 influenza virus in pasteurized milk does not cause adverse responses to subsequent influenza infection

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Pasteurisation: The First Line of Defense

The reassuring news is that pasteurisation works. This common heat treatment kills viruses and bacteria in milk, including the H5N1 strain. In other words, the cartons in your fridge are not contagious. Bird flu cannot be contracted when you drink milk available in the stores.

However, scientists observed something new—pasteurisation kills live viruses, but not all the fragments of it. Small fragments of viral proteins and genetic material can survive, and these can still react with our immune system.

What Happens When the Body Meets Viral Fragments?

In a recent mice study, mice fed pasteurised H5N1 milk did not get sick. But their bodies behaved as though they were met with a virus:

• The gut immune system lit up, showing signs of inflammation.
• Mice even produced antibodies, the protective proteins that fight infections.

This is because, in some cases, harmless viral debris in food can cause our bodies to overreact. In the short term, the response is not dangerous, but scientists do not yet know what it may entail in terms of long-term health.

Why Scientists Are Concerned

Until now, there is no evidence that bird flu can be transmitted to human beings via milk. Nevertheless, the appearance of the H5N1 in dairy cows is worrying. Viruses may be unpredictable, and every new jump across species poses new threats.

Researchers are interested in learning whether or not repeated exposure to viral fragments could:

• Alter the immune system over time
• Affect people with weakened immunity
• Increase the chances of the virus adapting further

This is why close monitoring of dairy herds, milk supplies, and farm workers has become a public health priority.

For Everyday Milk Consumers

The takeaway is simple:

• Pasteurised milk is safe. There’s no evidence it can give you bird flu.
• Raw, unpasteurised milk is riskier, not just for bird flu but for many other infections. Experts strongly advise against it.
• The bigger issue is what this viral crossover means for the future of food safety and pandemic preparedness.

Milk is safe to drink. However, the discovery of bird flu in cows highlights just how adaptable viruses can be—and why scientists remain on guard. While milk itself poses no transmission risk today, tomorrow’s threat may look different. Continued research, close monitoring, and caution are essential to stay prepared.

Reference:

1. Repeated oral exposure to H5N1 influenza virus in pasteurized milk does not cause adverse responses to subsequent influenza infection - (https://www.science.org/doi/10.1126/sciadv.aeb3906)

Source-Science Advances